This invention relates to novel camptothecin derivatives that are useful for treating various types of cancer.
Camptothecin (often abbreviated as xe2x80x9cCPTxe2x80x9d), a phytotoxic alkaloid first isolated from the wood and bark of Camptotheca acuminata (Nyssaceae) by Wall and coworkers in 1966, was shown to have antitumor activity against the mouse leukemia L1210 system. The compound has a pentacyclic ring system with an asymmetric center in ring E with a 20 S configuration. The pentacyclic ring system includes a pyrrolo [3, 4-b] quinoline (rings A, B and C), a conjugated pyridone ring D), and six membered lactone (ring E) with an 20S-hydroxyl group. Camptothecin itself is essentially insoluble in water. Therefore, camptothecin was evaluated clinically as a water soluble sodium carboxylate salt in the early stages. It appears that the carboxylate salt was actually the compound where the E ring was open to form the sodium salt. This sodium salt produced severe toxicity and had very little anticancer activity. Thus early work on camptothecin was discontinued after starting phase II trials. However, interest in the compound revived when it was found to inhibit topoisomerase, an enzyme that is required for its swiveling and relaxation of DNA during molecular events such as replication and transcription. A number of syntheses and modifications of the molecule have been reported in the literature and new derivatives have been prepared over the years. For example, topotecan (9-dimethylaminomethyl-10-hydroxy CPT) and irinotecan (7-ethyl-10[4-(1-piperidino)-1-piperidino] carbonyloxy CPT) show clinical useful activity. This invention defines a new series of 20 S esters that are useful for treating various types of cancer. The novel compounds have higher potency and lower toxocity than CPT and other CPT derivatives.
One aspect of this invention is a compound of the formula (I), below, 
wherein R is RaRbN(CH2)m, m is an integer of 1-10 (preferably 2), and each of Ra and Rb is independently
lower alkyl substituted with one to five substituents independently selected from the group consisting of halo, lower alkoxy, hydroxy, cyano, nitro, or amino;
phenyl optionally substituted with from one to five substituents independently selected from the group consisting of halo, lower alkyl, lower alkoxy, hydroxy, cyano, nitro, amino, halogenated lower alkyl, halogenated lower alkoxy, formyl, lower alkyl carbonyl, hydroxycarbonyl, lower alkylcarbonyloxy, benzyloxy, optionally substituted piperidino, lower alkoxycarbonyl, and lower alkylcarbonylamino;
cycloalkyl of 3-7 carbons, optionally substituted with one to five substituents independently selected from the group consisting of halo, lower alkyl, lower alkoxy, hydroxy, cyano, nitro, amino, halogenated lower alkyl, halogenated lower alkoxy, hydroxycarbonyl, lower alkoxycarbonyl, lower alkylcarbonyloxy, and lower alkylcarbonylamino;
lower alkoxy; or
RaRb together with N form a cyclic amine or imide ring;
R2 is hydrogen, halo, lower alkyl, lower alkoxy, hydroxy, RC(O)O (R defined hereinbefore), cyano, nitro, amino, halogenated lower alkyl, halogenated lower alkoxy, hydroxycarbonyl, xe2x80x94C(O)H, lower alkoxycarbonyl, tri lower alkylsilyl, lower alkylcarbonyloxy, lower alkylcarbonylamino, lower alkylcarbonyloxymethyl, substituted vinyl, 1-hydroxy-2-nitroethyl, alkoxycarbonylethyl, aminocarbonyl, alkylcarbonyl, alkylcarbonylmethyl, benzoylmethyl, benzylcarbonyloxymethyl, or mono- or di lower alkoxymethyl.
R3 is hydrogen, halo, lower alkyl, lower alkoxy, hydroxy, RC(O)O (R defined hereinbefore) cyano, nitro, amino, halogenated lower alkyl, halogenated lower alkoxy, hydroxycarbonyl, lower alkoxycarbonyl, CH2NR7R8 (where each of R7 and R8 is independently Hxe2x80x94, alkyl of 1-6 carbons, optionally substituted phenyl, hydroxy lower alkyl, amino lower alkyl, or mono- or dialkylamino lower alkyl, or R7 and R8 taken together with xe2x80x94Nxe2x80x94 represent a cyclic amino-), xe2x80x94C(O)H, CH2 R9 (where R9 is lower alkoxy, CN, amino lower alkoxy, mono- or di-lower alkylamino lower alkoxy, lower alkylthio, amino lower alkylthio, for mono- or di-lower alkylamino lower alkylthio), or NR10R11 (where each of R10 and R11 is independently hydrogen, lower alkyl, phenyl, hydroxy lower alkyl, amino lower alkyl, or mono- or di-lower alkyl, or R10 and R11 taken together with xe2x80x94Nxe2x80x94 represent a cyclic amino), dialkylamino alkyl, lower alkylcarbonyloxy, or lower alkylcarbonylamino; and
R4 is hydrogen, halo, lower alkyl, lower alkoxy, hydroxy, RC(O)O (R defined hereinbefore) cyano, nitro, amino, amino lower alkyl, halogenated lower alkyl, halogenated lower alkoxy, hydroxycarbonyl, lower alkoxycarbonyl, carbamoyloxy, lower alkylcarbonyloxy, or lower alkylcarbonylamino, or R4 together with R5 is methylenedioxy;
R5 is hydrogen, halo, lower alkyl, lower alkoxy, hydroxy, RC(O)O (R defined hereinbefore), cyano, nitro, amino, halogenated lower alkyl, halogenated lower alkoxy, hydroxycarbonyl, lower alkoxycarbonyl, lower alkylcarbonyloxy, or lower alkylcarbonylamino; and
R6 is hydrogen, halo, lower alkyl, lower alkoxy, hydroxy, RC(O)O (R defined hereinbefore), cyano, nitro, amino, halogenated lower alkyl, halogenated lower alkoxy, hydroxcarbonyl, lower alkoxycarbonyl, lower alkylcarbonyloxy, or lower alkylcarbonylamino.
Another aspect of the invention is a pharmaceutical composition useful for treating cancer in a warm-blooded animal, which composition comprises compound of the invention as defined herein in combination with a pharmaceutically acceptable excipient.
Another aspect of this invention is a method for treating cancer in a warm-blooded animal, which method comprises administering a therapeutically effective amount of a compound of the invention as defined herein. The compound is administered in a therapeutically effective dose by appropriate administration, e.g. orally, topically, or parenterally.
Another aspect of this invention is process for preparing compounds of this invention by reacting camptothecin (CPT) or a CPT analog with a compound of the formula Rxe2x80x94C(O)X, wherein R is RaRbN(CH2)2, where Ra and Rb are as defined herein, and X is e.g. bromide, chloride, hydroxy, alkoxy of 1-11 carbons.
Other aspects of this invention will be apparent to one of skill in the art by reviewing the ensuing specification.